Dayton ND25TA Tweeter Xmax

[Tenson]

In case anyone wanted to know, because it doesn't seem to be in the spec sheet, I took apart a ND25TA tweeter. The magnetic gap is 2mm, the voice coil is either 1mm (top layer) or 1.3mm(bottom layer). Thus Xmax is 1mm or 0.7mm (p-p).

The VC uses 0.13mm wire. It is double layer with 10 windings on the bottom and 8 windings on top.

 

[weltersys]

The magnetic gap is 2mm, the voice coil is either 1mm (top layer) or 1.3mm(bottom layer).

For a moment thought the Dayton ND25TA might use an upper (top) and lower (bottom) coil in a XBL² split gap motor like the Creative Sound Solutions LD25X, rather than the usual inner and outer layer.

So ~1.5mm one way excursion would ND25TA's drive the coil completely out of the magnetic gap?
Any estimate of Xmech, where the coil former, surround, or diaphragm would contact some part of the magnetic structure?

 

[Tenson]

I'd estimate >3 mm before the VC former hits the back. As for the suspension I'm really not sure.

I find the thinner magnet on top interesting. I don't think I've seen that in other small tweeters. Is it a bit like Purifi sticking a magnet on the pole piece? No copper here, though.

 

[weltersys]

I find the thinner magnet on top interesting. I don't think I've seen that in other small tweeters. Is it a bit like Purifi sticking a magnet on the pole piece?

The thinner piece looks like a pole piece extension made of the same steel, rather than another magnet.
The Vifa PL27TG-35 tweeter's pole piece also extends like the Dayton, though the Vifa uses a vent through the pole piece to increase the chamber volume, and is made as one piece, rather than two slugs glued together.

The Dayton tweeter pole piece extension would reduce it's chamber volume, and perhaps make the Bl(X) magnetic curve complement the Kms(X) compliance curve for better excursion symmetry, reducing distortion.

 

[b_force]

The distortion of most tweeters will go up well above where the excursion becomes a problem.

Although it depends, but roughly 1.5-2 times Fs is a decent rule of thumb.

I personally always just measure it (or look for online data).

Seems like the old rule of thumb wasn't so crazy.

 

[Tenson]

I'm pretty sure that's a magnet on top, it cracked in half.

 

[weltersys]

Whether the pole piece was extended with a steel slug or a magnet, there would be an increase in Bl on that side compared to without it.

How does the top magnet strength compare to the lower magnet?

 

[Tenson]

Wll, it's thinner. I can't say more more than that!